This invention relates to antenna systems, and more particularly to a metallic radome having a periodic array of slotted elements in its surface.
The study of metallic radomes has received increased emphasis in recent years. The increased interest in metallic radomes is largely due to their potential in overcoming the mechanical and electrical limitations of conventional dielectric radomes in high-speed, all-weather aircraft applications. A metallic radome offers the potential for greater overall mechanical strength and enhanced resistance to environmental stresses caused by rain, hail, dust and lightning, compared to conventional dielectric or ceramic radomes. The signal reception problem caused by static charge buildup and subsequent discharge to the airframe, encountered with dielectric radomes, could be eliminated by use of a metallic radome. A metallic radome could also better distribute frictionally induced heating arising from high speed flight. Finally, a metallic randome could conceivably be made lighter in weight than a dielectric radome.
The metallic radome concept also represents a useful alternative approach in overcoming the inherent electrical performance limitations of dielectric radomes. Most dielectric radomes are designed with a thickness of about a half-wavelength, to minimize impedance mismatch (i.e., reflection) losses. The optimum thickness, however, depends on the incidence angle, polarization, and frequency of the signal. Therefore, when the beam of the antenna enclosed by the radome is scanned, the radome introduces varying amounts of insertion loss and phase in the transmitted or received signals. The varying insertion phase is particularly troublesome, since it causes a change in the beam direction. This may in turn cause a significant deterioration in the performance of a tracking radar.
The metallic radome presented herein offers an improved transmission performance using a realistically streamlined radome shape. The novel slotted periodic surface design employed as the radome surface provides nearly ideal transmission properties for signal frequencies within its design band. The radome can accommodate scanning antennas transmitting arbitrarily polarized signals over an unrestricted range of scan angles.